The present invention concerns a tire with radial carcass reinforcement, more particularly a xe2x80x9cHeavy Dutyxe2x80x9d tire designed for mounting on vehicles such as trucks, road tractors, buses, trailers and others, and in which a new reinforcement structure of the beads is adopted with a view to improving the endurance of the said beads.
In general a tire of the type considered comprises a carcass reinforcement formed of at least one ply of metallic cables anchored in each bead to at least one bead wire with a turn-up. Radially above the carcass reinforcement is a crown reinforcement consisting of at lest two plies of metallic cables crossed from one ply to the next and forming angles between 10xc2x0 and 45xc2x0 relative to the circumferential direction. The turn-ups of the carcass reinforcement are generally reinforced by at least one ply of metallic cables orientated at a slight angle relative to the circumferential direction.
If only one bead reinforcement ply is present, this can be located along the carcass reinforcement turn-up with a radially upper end over or under the radially upper end of the turn-up of the carcass reinforcement. As for the radially lower end of such a ply, this is generally located either on a line parallel to the rotation axis and passing approximately through the center of gravity of the median section of the anchoring bead wire of the carcass reinforcement, in the case of a tire having beads designed to be mounted on rim seats inclined at 15xc2x0xc2x12xc2x0, or on a line parallel to the rotation axis passing through a point located between the center of gravity of the median section of the anchoring bead wire and the point where the axial width of the carcass reinforcement is widest, in the case of a tire having beads designed to be mounted on rim seats inclined at 0xc2x0 or at 5xc2x0xc2x11xc2x0. In this second case the bead reinforcement ply is then wrapped around the bead wire so that it has an axially outer part and an axially inner part, the radially upper end of the axially inner part generally being located below the radially upper end of the axially outer part.
The aim of the known solution is to avoid de-radialization of the carcass reinforcement turn-up cables and to minimize the radial and circumferential deformations undergone by the end of the said turn-up and by the layer of rubber outside which covers the bead and ensures its contact with the rim.
In other cases the metallic reinforcing ply has been replaced by several plies, for example made of textiles, located axially either on the same side as the turn-up or on either side thereof, or again partly along the turn-up and partly along the carcass reinforcement. Another variant consists in positioning two reinforcement plies along the turn-up on either side thereof, and a third ply along the carcass reinforcement axially on the outside.
The endurance of tire beads can also be improved by arranging along the carcass reinforcement two reinforcing plies, while the turn-up of the said reinforcement is not reinforced.
Due to the progress achieved and to the fact that certain types of rolling surfaces have been made less harsh where tire tread is concerned, the life of xe2x80x9cHeavy Dutyxe2x80x9d tires has become such that it is again necessary to improve the bead endurance, more especially in tires subjected to prolonged rolling which often results in high bead temperatures by virtue of the temperatures reached by the rims to which they are fitted.
According to French patent application FR 2 730 190 the said improvement can be achieved by the presence in the beads of at least one reinforcement ply formed of circumferential metallic elements wrapped around the bead wire outside the rolled-up part of the carcass reinforcement, such that the ends, respectively, of the axially outer and axially inner parts are radially located above a line parallel to the rotation axis and passing through the point of the bead wire furthest from the said rotation axis. As is known, the carcass reinforcement, formed of radial wires or cables is therefore at the level of its contact surface with the bead wire formed of essentially circumferential elements which are generally metallic in the form of wires, cables, ribbons or rolled-up strips inserted between the said elements with essentially circumferential orientation and the additional ply of metallic elements, they too being circumferential. This structure therefore enables the tensile forces undergone by the carcass reinforcement to be absorbed and so minimizes all the deformations at the ends of the carcass reinforcement turn-up regardless of the rolling conditions.
The same application FR 2 730 190 describes an advantageous variant for reinforcing the bead, in which the end of the axially inner part of the ply of circumferential elements is covered by a reinforcing ply 9 consisting of radial metallic cables.
To obtain more effective stiffening of the beads and the low parts of the side-walls of a tire with radial carcass reinforcement, the patent FR 1 594 780 proposes that the bead reinforcement armatures, located axially outside the main part of the carcass reinforcement and axially inside the turn-up of the said reinforcement, should consist of radial reinforcement elements.
To improve the endurance of the beads of radial tires for heavy vehicles, application EP 0 202 925 also proposes the use of two additional bead reinforcement armatures, a first consisting of metallic elements and a second armature of elements inclined relative to the median direction, such that the radial positions of the radial ends of the said armatures are specified.
This invention proposes another solution, which is technically and industrially optimum for tires with beads designed to be mounted on rims of the type called flat or whose rim seats are inclined at 5xc2x0.
To improve the endurance of a tire designed to carry heavy loads, according to the invention the said tire comprises at lest one radial carcass reinforcement formed of at least one ply of inelastic reinforcing elements anchored in each bead to a bead wire to form a turn-up whose end is located at a radial distance HRNC from the base of the bead, and each bead is reinforced by at least two additional reinforcement armatures, at least one first armature formed of a single ply of radial inelastic metallic reinforcing elements wrapped around the anchoring bead wire of the carcass reinforcement outside the said carcass reinforcement and forming two parts such that the radially upper end of the axially outer part is located radially a distance HLE from the base of the bead equal to at least 65% of the distance HRNC, and at least one second armature formed of elements which make an angle a with the circumferential direction such that 0xc2x0xe2x89xa6xcex1xe2x89xa645xc2x0, characterized in that when viewed in median section, the second additional bead reinforcement armature, which is not wrapped around the said anchoring bead wire, is formed of at least one ply of circumferential metallic reinforcement elements, which are sections or bundles of sections of metallic cables whose circumferential length is smaller than the circumferential length of the median axis of the bead wire.
Reinforcement elements are considered radial if the angle they make with the tire""s circumferential direction is within the range 80xc2x0-100xc2x0.
The term xe2x80x98armature wrapped around the bead wirexe2x80x99 means an armature forming two parts, an axially inner and an axially outer part, whose respective ends are radially above a line parallel to the rotation axis and passing through the center of gravity of the cross-section of the anchoring bead wire.
Similarly, in the context of the invention, the radially upper end of the part of a bead reinforcement armature which can consist of one or more plies is understood to mean the end of the armature ply furthest from the rotation axis, and the armature plies can have upper ends within a radial distance range of at most 20 mm. Likewise, the radially lower end of a bead reinforcement armature is the lower end of the ply least distant from the rotation axis.
The first armature of radial reinforcing elements preferably has the end of its axially inner part located between the line parallel to the rotation axis and passing through the center of gravity of the cross-section of the bead wire and the line parallel to the said rotation axis and passing through the point where the carcass reinforcement is axially widest. The radially upper end of the axially outer part is then preferably located a radial distance from the base of the bead between 65% and 95% of the distance HRNC separating the turn-up end of the carcass reinforcement from the said base.
According to a second aspect of the invention, the second armature is formed of two plies of reinforcing elements parallel to one another within each ply, crossed from one ply to the next, and making an angle of 45xc2x0 with the circumferential direction, as measured at the radially lower edges of the said two plies. The reinforcing elements are advantageously wires or textile cables, and the said structure of the second armature is particularly advantageous in the case when the first bead reinforcement armature consists of textile reinforcing elements. The end of the axially outer part can be located a radial distance from the base of the bead greater than the distance HRNC, while remaining smaller than the radial distance separating the said base from the end of the axially inner part.
Whether made of textile or metal, the second armature is advantageously arranged either axially inside or axially outside the part of the carcass reinforcement not turned up, with a radially upper end closer to the rotation axis than is the upper end of the axially inner part of the armature of radial elements.
When it is positioned axially inside the carcass reinforcement, the second armature is preferably between the said part of the carcass reinforcement not turned up and the first armature of radial reinforcement elements.